View Full Version : Check headspace???
coolcraigster
06-28-21, 20:01
So i see alot of people say you need to check headspace between bolt and barrel after assembling new rifle. Also see alot of people say dont worry about it as long as you are using parts from reputable manufacturers. So I just finished my 3rd build... should I buy the gauges and check it? What do yall do?
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gunnerblue
06-28-21, 20:30
So i see alot of people say you need to check headspace between bolt and barrel after assembling new rifle. Also see alot of people say dont worry about it as long as you are using parts from reputable manufacturers. So I just finished my 3rd build... should I buy the gauges and check it? What do yall do?
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I only use 5.56mm chambers and all I do is check headspace with a field gauge (Brownells carries them).
A lot of folks will buy both barrels and bolts from the same manufacturer and not worry about checking headspace- to me a gauge is cheap insurance
I check headspace. I see literally no downsides to it from a QC viewpoint.
coolcraigster
06-28-21, 22:12
I've heard of GO and NOGO gauges but not a Field gauge. Whats the difference?
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I check headspace on everything I build or service. It's easy to do and is an indicator of reliability and safe operation. A good set of headspace gauges will last you a lifetime.
coolcraigster
06-28-21, 22:22
I check headspace on everything I build or service. It's easy to do and is an indicator of reliability and safe operation. A good set of headspace gauges will last you a lifetime.Which gauges do you use?
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I've heard of GO and NOGO gauges but not a Field gauge. Whats the difference?
This may help.
Headspace gauges are for ALL guns especially BELT FEDS. ;)
So my USGI issue 5.56mm FIELD gauge which is cutout for the extractor and ejector is now inaccurate because the 'interwebs' said so. Which way is it inaccurate? Does it say headspace is too tight when it's really excessive or is it indicating it's too big when it's still safe? Or do you not really know?
Military GO 1.4646" - 1.4648"
Military NOGO 1.4704" - 1.4706"
Military FIELD 1.4728" - 1.4730"
Colt's FIELD II 1.4736" 1.4736"
For those curious about belt fed head space.
M249 SAW GO 1.4940" - 1.4947"
M249 SAW NOGO 1.4980" - 1.4982"
M249 SAW FIELD 1.50196" - 1.50216"
A picture is worth a thousand words here.
https://d2j6dbq0eux0bg.cloudfront.net/images/812059/2373712483.jpg
https://www.forsterproducts.com/pdf/brochures/hi-res-for-print/Forster-Products-NATO%20Chamber%20Headspace%20Gages%20Sales%20Sheet_NATO-001_Issue%204_July%202018_print.pdf
Which gauges do you use?
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I have sets of Forster gauges, Go, No Go, Field. If you purchase headspace gauges, do not mix brands.
Straight Shooter
06-29-21, 08:26
What about for WYLDE chambers...are there gauges for those?
coolcraigster
06-29-21, 09:06
I have sets of Forster gauges, Go, No Go, Field. If you purchase headspace gauges, do not mix brands.I'm kinda confused on the field gauge still. So it should close on the GO gauge, shouldn't close on the NO GO gauge. So if it closes on NO GO it fails correct? Why is there another gauge (Field) past NO GO if its not even supposed to close on NO GO?
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Go and No-Go are used for manufacturing a rifle or replacing a bolt or barrel.
Field is the max before being considered worn out or unsafe. It doesn’t really happen with modern designs and metallurgy much.
A picture is worth a thousand words here.
https://d2j6dbq0eux0bg.cloudfront.net/images/812059/2373712483.jpg
https://www.forsterproducts.com/pdf/brochures/hi-res-for-print/Forster-Products-NATO%20Chamber%20Headspace%20Gages%20Sales%20Sheet_NATO-001_Issue%204_July%202018_print.pdf
Not quite accurate.
SAAMI is 1.4636” to 1.4736”, though it’s unlikely anything is actually made near the high limit.
Acceptance requirements for the M16/M4 is 1.4656” to 1.4706”.
The second is what a new AR should measure, so get gauges with the actual number on them or from a manufacturer that states what size their Go and No-Go are.
coolcraigster
06-29-21, 11:16
So do yall recommend just getting GO and NO GO gauges or getting the Field gauges as well? I have 556 and 223 wydle chambers. Im guessing one set of gauges will work for both??? Also have a 300 BLK.
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gunnerblue
06-29-21, 12:10
So do yall recommend just getting GO and NO GO gauges or getting the Field gauges as well? I have 556 and 223 wydle chambers. Im guessing one set of gauges will work for both??? Also have a 300 BLK.
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https://www.m4carbine.net/showthread.php?191984-223-vs-5-56-go-no-gauges
Here's a thread from back when Iraqgunz was still with us. Good info.
The field gauge tells you that your chamber is unsafe and is, still I believe, the only gauge used by the military.
Also, checking headspace with a fully assembled bolt can give a false reading due to the spring pressure of the ejector
What about for WYLDE chambers...are there gauges for those?
I use regular .223 gauges.
[QUOTEThe field gauge tells you that your chamber is unsafe and is, still I believe, the only gauge used by the military.
Also, checking headspace with a fully assembled bolt can give a false reading due to the spring pressure of the ejector[/QUOTE]
66039
If you have check head space frequently turning or having your gauge turned so you don’t have to strip the bolt is a huge convenience.
I have 556 and 223 wydle chambers. Im guessing one set of gauges will work for both??? Also have a 300 BLK.
5.56 and any .223 chamber all headspace the same. The difference is in the neck and throat, while headspace is where the shoulder is set.
300 BLK will need to use 300 BLK gauges.
For those curious about belt fed head space.
M249 SAW GO 1.4940" - 1.4947"
M249 SAW NOGO 1.4980" - 1.4982"
M249 SAW FIELD 1.50196" - 1.50216".
This is wrong, or at least, very misleading.
The M16, C.I.P., and SAAMI all use a 0.330" reference diameter for measuring headspace. For unknown reasons, FN uses a 0.300" reference diameter for measuring headspace, so they appear longer.
They are actually shorter. If you measure the M249 gauges to a 0.330" reference diameter you get these dimensions:
M249 SAW GO 1.4609" to 1.4611"
M249 SAW NOGO 1.4647" - 1.4649"
M249 SAW FIELD 1.4686" - 1.4688"
You might note that all of these are a good bit shorter than an M16 or SAAMI .223
https://i.imgur.com/0klTMgb.png
It is ideal to have all three gages. GO, NO GO and Field. The Field is important if the NO GO gage goes. The Field gage as already said will tell you if the rifle if safe to shoot. As long as the Field does not go, then you are safe to shoot. Some manufacturers like Faxon even state that it is not uncommon for the NO GO gage to go and that the barrel is still good to go as long as the Field does not go.
This is wrong, or at least, very misleading.
Surprising given the credentials of who I quoted. Correction noted. Why is the M249 chamber shorter?
Surprising given the credentials of who I quoted. Correction noted. Why is the M249 chamber shorter?
It is wrong because the person giving the information only gave you half the information. If you convert the length as shown in millimeters to inches, you get the numbers he quoted, he just did not bother to convert the reference diameter.
As to why . . . This article gives some background information and part of the reason, in that a short chamber prevents excessive case stretch. (https://www.m14forum.com/threads/bolt-over-travel-or.514133/) You also have to remember that the clearances around a machine gun's locking lugs are generous, as they have to contend with dirt and muck dragged into the action by the belt.
The other part of the reason is that machine guns tend to have a lot of energy in the bolt, they usually have a 200 round belt lift requirement. Because of the energy requirements, they tend to have high bolt closing velocities. Something has to stop the bolt's forward motion, and that something is going to get beat to **** after repeated impacts. So, they allow the cartridge case to absorb some of the energy when the shoulder gets set back.
the AR-15 Junkie
06-30-21, 22:16
I have sets of Forster gauges, Go, No Go, Field. If you purchase headspace gauges, do not mix brands.
Whats wrong with mixing brands? If they are machine to spec why would it matter?
5.56 and any .223 chamber all headspace the same. The difference is in the neck and throat, while headspace is where the shoulder is set.
300 BLK will need to use 300 BLK gauges.
Thanks, Todd
Andy
Whats wrong with mixing brands? If they are machine to spec why would it matter?
I don't mix brands based on a recommendation made to me over 30 years ago from a good gunsmith. It was also mentioned in a Brownell's newsletter I received a few years back. Uniformity of work was mentioned in the article. https://www.brownells.com/aspx/learn/learndetail.aspx?lid=12555
I don't mix brands based on a recommendation made to me over 30 years ago from a good gunsmith. It was also mentioned in a Brownell's newsletter I received a few years back. Uniformity of work was mentioned in the article. https://www.brownells.com/aspx/learn/learndetail.aspx?lid=12555
To be fair, the industry has progressed a bit in the last 30 years.
Whats wrong with mixing brands? If they are machine to spec why would it matter?
Because the "specifications" are internal to the gauge manufacturer. If you take a PTG .223 Remington GO gauge over to Forster and have Forster check it for conformity, it may not pass. This is less of a problem since 2015 when SAAMI started to publish recommended headspace gauge drawings with tolerancing, and material properties. (It is still voluntary though.)
This is different from US military gauges, in that it is mandatory that all made to a common drawing, and common standard.
Because the "specifications" are internal to the gauge manufacturer. If you take a PTG .223 Remington GO gauge over to Forster and have Forster check it for conformity, it may not pass.
Despite the differences if they both confirm a valid chamber what is the problem with mixing? If one of them does not then isn't it a faulty gauge? I don't see how tolerance stacking applies here.
To be fair, the industry has progressed a bit in the last 30 years.
Because the "specifications" are internal to the gauge manufacturer. If you take a PTG .223 Remington GO gauge over to Forster and have Forster check it for conformity, it may not pass. This is less of a problem since 2015 when SAAMI started to publish recommended headspace gauge drawings with tolerancing, and material properties. (It is still voluntary though.)
This is different from US military gauges, in that it is mandatory that all made to a common drawing, and common standard.
Yes sir it has. That's why I posted the link to the Brownell's article, it's a lot more current.
Yes sir it has. That's why I posted the link to the Brownell's article, it's a lot more current.
Not by much, the article was written over twenty years ago. (The .PDF was created on 15 February 2002, and I have a hard copy of it from around 1999.)
Like I noted, IF all the various gauge manufacturers use the SAAMI drawings provided in ANSI SAAMI Z299.4-2015 - "Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Rifle Ammunition for the Use of Commercial Manufacturers" (published 14 December 2015), you probably could buy from different manufacturers. But, the first word in the title suggest the safe thing is to stick to the same maker.
https://i.imgur.com/kxHGx03.png
Despite the differences if they both confirm a valid chamber what is the problem with mixing? If one of them does not then isn't it a faulty gauge? I don't see how tolerance stacking applies here.
Colt's "FIELD" gauge is 1.4736"
SAAMI's "FIELD" gauge is 1.4700"
Apparently, not everyone is on the same bandwagon, at least, not yet.
Lysander,
I ran into a situation where I could not find Go, No-Go and Field gauges for 6.5 Creedmoor all made by the same company, so I decided to wait until I was able to purchase all three gauges made by the same manufacturer. Would you be comfortable mixing Pacific Tool and Gauge with Clymer headspace gauges or Clymer with Forster gauges?
Something as new as Creedmoor would probably be okay.
Something like .300 Blackout, that doesn't have a SAAMI standard, no.
300 Blackout is SAAMI.
I don’t have any brand mixing concerns, but I do require the actual number on gauges.
300 Blackout is SAAMI.
I don’t have any brand mixing concerns, but I do require the actual number on gauges.
.300 Blackout does not have SAAMI approved headspace gauges, therefore there can be wide variation in GO, NOGO, and FIELD lengths.
Look it up.
gunnerblue
07-02-21, 17:36
.300 Blackout does not have SAAMI approved headspace gauges, therefore there can be wide variation in GO, NOGO, and FIELD lengths.
Look it up.
PTG sells gauges made to the SAAMI specifications for 300 BLK
gunnerblue
07-02-21, 17:39
5.56 and any .223 chamber all headspace the same. The difference is in the neck and throat, while headspace is where the shoulder is set.
300 BLK will need to use 300 BLK gauges.
I understand what you are saying, but to the uninitiated I think this is a little misleading. 5.56 and .223 chambers should be checked by their own respective gauges.
.300 Blackout does not have SAAMI approved headspace gauges, therefore there can be wide variation in GO, NOGO, and FIELD lengths.
Look it up.
So does SAAMI actually approve headspace gauges for anything? When I tried looking it up, I found this FAQ:
https://saami.org/faqs/#1622648797091-fd1263a1-69ea
My read is that SAAMI defines min and max chamber lengths, but it’s up to the firearm manufacturer to decide where within that range they want their chambers to land, and to gauge accordingly. And the notion of a “field gauge” is explicitly not endorsed.
So does SAAMI actually approve headspace gauges for anything? When I tried looking it up, I found this FAQ:
https://saami.org/faqs/#1622648797091-fd1263a1-69ea
My read is that SAAMI defines min and max chamber lengths, but it’s up to the firearm manufacturer to decide where within that range they want their chambers to land, and to gauge accordingly. And the notion of a “field gauge” is explicitly not endorsed.
Look up the 2015 (or later) editions of the SAAMI Z299 Series, Voluntary Industry Performance Standards for Pressure and Velocity
Z299.1 - Rimfire
Z299.2 - Shotshell
Z299.3 - Centerfire Pistol and Revolver
Z299.4 - Centerfire Rifle
Headspace gauge data starts on page
Z299.1 - 70 (77 in .pdf)
Z299.2 - 101 (108)
Z299.3 - 122 (131)
Z299.4 - 212 (224)
PTG sells gauges made to the SAAMI specifications for 300 BLK
Just like "mil-spec" . . . . meaningless marketing.
SAAMI does not have a specification for a .300 Blackout headspace gauge, they only specify the chamber dimensions. This is why multiple manufacturer's could have multiple gauges with slight differences, such as tolerancing, finish, material, hardness, etc . . .
AND, there is no such thing as a 5.56mm NATO headspace gauge.
There are M16 gauges
There are M249 gauges
There are M27 gauges
etc.
.300 Blackout does not have SAAMI approved headspace gauges, therefore there can be wide variation in GO, NOGO, and FIELD lengths.
Wide? Go and No-Go have to be within the 0.010” chamber depth tolerance of SAAMI or they are not 300BLK gauges.
Insist on gauges with the actual headspace number, so you will know how much less than maximum the No-Go (likely) is.
Field gauges are a relic of the past like proof load testing, when poor designs, questionable material and hardening processes were the norm.
Headspace gauge data starts on page
[…]
Z299.4 - 212 (224)
Thanks — I had missed that section. It does give a blueprint for the gauge, but as far as I can see SAAMI remains essentially silent on the question of what length dimensions to use for “GO” and “NOGO” (never mind “FIELD”). They just have to be somewhere between chamber MIN and MAX.
So e.g. if I wanted to emulate what Sam Colt and Uncle Sam use for the M16 chamber, I could make a pair of gauges per the Z299.4 print, one with F=1.4646 and another with F=1.4706, labeled “Sams GO 223 Rem” and “Sams NOGO 223 Rem” respectively, and that would comply with SAAMI guidance.
My point is basically to echo Todd.K: if the gauge doesn’t have a length marked on it, it’s hard to know what you’ve got. If it’s a military gauge made to a specific drawing, great. But if it’s a commercial gauge that just says “NOGO” or whatever, it could be almost anything, even for a SAAMI-supported cartridge.
Insist on gauges with the actual headspace number, so you will know how much less than maximum the No-Go (likely) is.
Field gauges are a relic of the past like proof load testing, when poor designs, questionable material and hardening processes were the norm.
I have a 1.4696 gauge. Is this useful or not?
gunnerblue
07-03-21, 13:14
Just like "mil-spec" . . . . meaningless marketing.
SAAMI does not have a specification for a .300 Blackout headspace gauge, they only specify the chamber dimensions. This is why multiple manufacturer's could have multiple gauges with slight differences, such as tolerancing, finish, material, hardness, etc . . .
Ah...I see what you mean now. I'd guess that if one were to do their due diligence one might find an appropriate set of gauges from certain manufacturers.
I have a 1.4696 gauge. Is this useful or not?
Sure, it could be. Kinda depends on what you’re trying to figure out.
If a chamber won’t take that gauge, then at least you know it’s not too loose. For comparison, SAAMI max chamber for 223 Rem is 1.4736, so if your gauge doesn’t go, then you’re well under that limit. And as I understand it, Colt’s max chamber for a new M16 is 1.4706, and so you’re under that too. (But the chamber might be too short.)
If the gauge does go, then you know the chamber is on the looser side, but you don’t know by how much, just that it’s longer than 1.4696, maybe by a little or maybe by a lot.
Just like "mil-spec" . . . . meaningless marketing.
SAAMI does not have a specification for a .300 Blackout headspace gauge, they only specify the chamber dimensions. This is why multiple manufacturer's could have multiple gauges with slight differences, such as tolerancing, finish, material, hardness, etc . . .
Which gauges, other than .300 Blackout headspace gauges, should we be concerned about?
Thanks — I had missed that section. It does give a blueprint for the gauge, but as far as I can see SAAMI remains essentially silent on the question of what length dimensions to use for “GO” and “NOGO” (never mind “FIELD”). They just have to be somewhere between chamber MIN and MAX.
So e.g. if I wanted to emulate what Sam Colt and Uncle Sam use for the M16 chamber, I could make a pair of gauges per the Z299.4 print, one with F=1.4646 and another with F=1.4706, labeled “Sams GO 223 Rem” and “Sams NOGO 223 Rem” respectively, and that would comply with SAAMI guidance.
My point is basically to echo Todd.K: if the gauge doesn’t have a length marked on it, it’s hard to know what you’ve got. If it’s a military gauge made to a specific drawing, great. But if it’s a commercial gauge that just says “NOGO” or whatever, it could be almost anything, even for a SAAMI-supported cartridge.
SAAMI MIN is the shortest chamber that SAAMI feels is safe from pinching the case neck and causing overpressure.
SAAMI MAX is the longest chamber SAAMI feels is safe from case separation, akin to the the military FIELD.
"GO" and "NOGO" are manufacturing limits and are usually decided on for maximum accuracy, longevity, and acceptable tolerances for the price point. "NOGO" being the maximum the factory will send out the door on new production. This intermediate gauge length is actually of little use to the average shooter, because you (the shooter) may not have access to all the information behind the choice of factory headspace dimensions. For example, if I shoot thousands of rounds in developing my new rifle and find that best accuracy is at a headspace of 1.4640" and 1.4710", and so I make barrels that headspace out to GO = 1.4640", and NOGO = 1.4710". Of course, Bubba will immediately get on the internet and complain that some barrels will not accept a USGI M16 MIN (1.4646"), and some barrels are above USGI M16 NOGO limit (1.4703"), never mind the fact that they are well inside the SAAMI limits (1.4636 - 1.4736") and M16 FIELD (1.4730"), so safe.
Generally, all the shooting public needs is the SAAMI MAX and MIN for any caliber, and if you build your own barreled actions, or match bolts, you probably want a set that goes from MIN to MAX in 0.001" steps, so you can actually measure your headspace to within a thousandths of and inch.
USGI M16 headspace gauges are actually pointless in my opinion. The entire range of USGI M16 gauge lengths fall inside the SAAMI safe limits.
In short, don't over complicate things.
https://i.imgur.com/KGgSNHC.png
Nice explanation, and with one possible exception, I think we’re seeing eye-to-eye on this stuff.
USGI M16 headspace gauges are actually pointless in my opinion.
I have no insight into how Colt chose the M16’s GO and NOGO dimensions, but it doesn’t seem crazy to me to put GO a little bigger than MIN to maybe help accommodate some crud in the chamber, or to put NOGO a little smaller than MAX to allow for wear. I wonder though whether Colt even uses such a gauge in practice — based on something you’ve posted previously, it sounds like they might actually gauge the barrel assembly and bolt separately.
you probably want a set that goes from MIN to MAX in 0.001" steps, so you can actually measure your headspace to within a thousandths of and inch.
https://i.imgur.com/KGgSNHC.png
Is there a set you recommend?
Nice explanation, and with one possible exception, I think we’re seeing eye-to-eye on this stuff.
I have no insight into how Colt chose the M16’s GO and NOGO dimensions, but it doesn’t seem crazy to me to put GO a little bigger than MIN to maybe help accommodate some crud in the chamber, or to put NOGO a little smaller than MAX to allow for wear. I wonder though whether Colt even uses such a gauge in practice — based on something you’ve posted previously, it sounds like they might actually gauge the barrel assembly and bolt separately.
They do.
This for the assembled barrel and extension:
http://pacifictoolandgauge.com/4254-large_default/ar15-ar10-extension-headspace-gauge.jpg
And, this for the bolt
https://i.imgur.com/pC1nTYQ.png
Is there a set you recommend?
The usual US makers.
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